You need to make sure that vars.txt has been created. If not that's probably the cause of the problem. Check that the directory where you have the script is writable. Try setting the permissions to 755 (rwxr-xr-x) or 777 (rwxrwxrwx).

Normally you need not create any of the other files the script uses. The firstrun.cgi script will create vars.txt if permissions are correct and it can actually create the file. All other files are created as they are needed for the first time (banned.txt, confirm.txt, subscribers.txt).